@mixin size ($width,$height){
    width: $width;
    height: $height;
}
@mixin  center {
    text-align: center;
}
@mixin  margin($shangxia,$zuoyou) {
    margin-top: $shangxia;
    margin-bottom: $shangxia;
    margin-left: $zuoyou;
    margin-right: $zuoyou;
}
@mixin padding($shangxia, $zuoyou) {
    padding-top: $shangxia;
    padding-bottom: $shangxia;
    padding-left: $zuoyou;
    padding-right: $zuoyou;
}
@mixin flex ($jc,$w,$d){
    display: flex;
    justify-content: $jc;
    align-items: center;
    flex-flow:$w $d ;
}
